I. Field of the Invention
The present invention generally relates to devices, systems, and methods for diagnosing and/or treating the heart. In a particular embodiment, the invention provides techniques for localizing and/or treating arrhythmias.
Significant progress has recently been made toward effective treatments of many cardiac arrhythmias. Contraction of a healthy human heart generally propagates through the heart tissue from the sinus node in the right atrium, and eventually the associated ventricles. This normal propagation of contraction forces blood to flow from the atria to the ventricles in a synchronized pumping action. Arrhythmias of the heart often originate at and/or propagate from alternative heart tissues, resulting in rapid irregular or regular contractions of some or all of the heart. Radiofrequency intracardiac catheter ablation of the alternative ectopic origin, an abnormal contraction pathway, or an abnormal pathway exit site is now used to effectively treat a variety of arrhythmias.
Although quite effective, current catheter ablation for treatment of cardiac arrhythmias has significant disadvantages. A particular challenge in an effective catheter ablation treatment is the time required for proper identification of the treatment site. As it is generally desirable to limit the size of the ablation, significant time is often spent testing candidate ablation sites. The testing often involves pacing, in which an artificial arrhythmia is initiated with a small electrical pulse from a catheter. The candidate sites are often tested sequentially by positioning the intracardiac catheter against a site within (for example) the right ventricle, identifying the engaged tissue location within the ventricle, sensing and/or pacing the heart cycles at the candidate site, repositioning the intracardiac catheter to a new candidate site, and repeating this process until an ectopic origin or an abnormal pathway exit site has been identified.
As fluoroscopy is often used to identify the location of the engaged tissue, this sequential iterative process can result in significant exposure of the patient and treating personnel to potentially harmful radiation. While alternative (and more complex) intracardiac catheter probe structures have been proposed to allow more rapid identification of the ectopic origin(s) of ventricular tachycardias (VTs) and other focal or re-entrant arrhythmias, the size and cost of these complex structures may limit their acceptability.
To overcome the disadvantages associated with the known, time consuming and/or invasive intracardiac arrhythmia sensing and localization techniques, researchers have been working on alternative arrhythmia localization techniques which rely on body surfacing mapping, often during pacing. Electrocardiograms (ECG) may be recorded during abnormal atrial or ventricular activity and compared with ECGs taken during pacing at different sites within the heart to help identify the ectopic or exit site, with the ECGs optionally taken using a standard 12-lead ECG system. More detailed information regarding ectopic or exit sites can be obtained by recording heart cycle signals at the body surface using a more comprehensive sensor array (sometimes called body surface ECG mapping). These heart cycle signals, which generally comprise small amplitude variations in electrical potential along the anterior and/or posterior torso, can be manipulated and/or mapped so as to provide an indication of the origin of the arrhythmia within the heart. Much of this work has concentrated on VT. More recent work has begun to investigate the possibility of localizing certain atrial arrhythmias, such as right atrial tachycardia. U.S. Provisional Patent Application No. 60/189,610, previously incorporated by reference, describes exemplary methods and systems for localization and treatment of atrial fibrillation.
While the new body surface mapping techniques appear quite promising, the previously proposed localization techniques generally have significant limitations. Specifically, many previous techniques involve comparison of ECG morphology or body surface map shape of the patient during an arrhythmia to a series of discrete known maps or plots of heart signals from previous pacing tests. The known map which most nearly matches the map of the patient is selected, and the ectopic or exit site of the patient is then initially assumed to be the same as a known ectopic or exit site associated with the selected known map. Unfortunately, although such methods are quite effective at identifying an arrhythmogenic region within a chamber of a heart, there will often be significant differences between a particular patient""s ECG morphology or body surface map (and the associated ectopic or exit site) and the discrete contents of any database.
In light of the above, it would be beneficial to provide improved devices, systems, and methods for localizing and/or treating arrhythmias within a heart of a patient. It would be particularly beneficial to provide methods and systems which could help locate ectopic and exit sites from across a continuous region of tissue, rather than merely selecting a candidate region from a group of discrete results. The present invention provides such improvements, mitigating and/or overcoming at least some of the disadvantages of known approaches for diagnosing and treating arrhythmias.
II. Related Art
The following patents may be relevant to the subject matter of the present invention, and their full disclosures incorporated herein by reference: U.S. Pat. No. 5,311,873; and U.S. Pat. No. 5,634,469. Peeters, H.A.P., SippensGroenewegen, A. and others described xe2x80x9cClinical Application of an Integrated 3-Phase Mapping Technique for Localization of the Site of Origin of Idiopathic Ventricular Tachycardiaxe2x80x9d in Circulation, 99:1300-1311 (1999). SippensGroenewegen, A. et al. also described xe2x80x9cBody Surface Mapping of Atrial Arrhythmias: Atlas of Paced P wave Integral Maps to Localize the Focal Origin of Right Atrial Tachycardiaxe2x80x9d, in J. Electrocardiol., 31(Supp.):85-91 (1998). Related work was described by SippensGroenewegen, A. et al. in, xe2x80x9cValue of Body Surface Mapping in Localizing the Site of Origin of Ventricular Tachycardia in Patients with Previous Myocardial Infarctionxe2x80x9d, J. Am. Coll. Cardiol. 24:1708-1724 (1994). Each of these references is incorporated herein by reference.
The present invention provides improved systems, devices, and methods for localizing and/or treating arrhythmias of a heart of a patient. Advantageously, the techniques of the present invention generally make use of heart signals sensed on an accessible body surface, generally using an array of heart sensors distributed across a torso of the patient. The invention often makes use of a database of known heart signals and associated ectopic sites or exit sites. Rather than merely selecting a discrete known ectopic or exit site associated with heart signals most nearly matching those of a particular invention, the invention can provide continuous localization to identify candidate ectopic or exit sites throughout a continuous region of tissue.
The known and measured heart signals may be compared by generating integral body surface maps of the patient""s torso from a selected time interval of a reference heart cycle. A body surface map for the patient is then statistically compared with the database of known signals. The statistical comparison allows interpolation of a candidate ectopic or exit site which is different than the known ectopic or exit sites from the database. This method is particularly advantageous for relative localization when at least one of the known ectopic or exit sites (and the associated known heart signals) are based on measurements taken from the patient undergoing diagnosis and/or treatment. In other embodiments body surface potentials may be sensed and/or mapped at a single time.
In a first aspect, the invention provides an arrhythmia localization method making use of a database. The database includes known heart signals and associated discrete known ectopic or exit sites. The arrhythmia localization method comprises measuring heart signals during an arrhythmia, and identifying a candidate ectopic or exit site which is different than the known sites by comparing the measured heart signals to a plurality of the known heart signals.
The heart signals may be sensed with an array of sensors distributed across an accessible body surface. The array will often have at least 6 sensing locations distributed across a torso of the patient. Preferably, a selected portion of the measured heart signals from a desired reference heartbeat are integrated at each sensing location to determine an associated integral value. The reference heartbeat may include a premature atrial beat or the initiation of an arrhythmia (particularly for atrial fibrillation), and a data matrix is generated by arranging the integral values according to their associated sensing locations. The data matrix is compared with data matrices of the database generated from the known heart signals. The comparison includes statistical interpolation between a plurality of the known sites to identify the candidate ectopic or exit site. Optionally, correlations between the known heart signals and known sites of the database are determined, facilitating the statistical comparison of the measured heart signals with the known heart signals.
Typically, the database will be normalized by transforming the known sites into a uniform coordinate system. Radial coordinate systems such as a polar coordinate or a cylindrical coordinate system are particularly beneficial, with the exemplary uniform coordinate system comprising a cylindrical coordinate system having an axis extending from an apex of the lower heart chamber to a mitral or tricuspid valve ring, with positioning along the axis often being normalized based on a distance between these two structures. Radial positioning of the axis may be relative to an aortic or pulmonic valve ring. In many embodiments, a position of a chamber of the heart of the patient will be established by identifying datum locations of the chamber, for example, by identifying an apex of a ventricle, a center of a mitral or tricuspid valve, and a center of an aortic or pulmonic valve. This facilitates applying the normalized database from the uniform coordinate system to a particular patient""s anatomical geometry.
Paced heart signals will often be measured by initiating an artificial arrhythmia at a pacing site of the patient. The candidate site identification will often be based at least in part on these paced signals. The candidate site will often be determined by calculating an estimated ectopic or exit site using the measured heart signals and the known heart signals. An estimated pacing site may also be calculated from the paced heart signals and the known heart signals. The estimated site can be modified to generate the candidate site based on, for example, a difference between the estimated pacing site and the actual pacing site. In general, the methods and systems of the present invention will benefit from accurate determinations of actual positions within a heart, which may be provided using biplane fluoroscopy, magnetic position sensing, ultrasound position sensing, electrical position sensing, or the like. Initiating a plurality of artificial arrhythmias at a plurality of pacing sites of the patient may allow identification of the candidate site using the pacing data. In fact, the database may be specific for the patient of interest and based entirely on paced data from the patient.
In many embodiments, a heart tissue will be imaged and the candidate site will be graphically indicated on an image of the heart tissue. The image will preferably comprise a three-dimensional image, most often being a biplane fluoroscopic images, and the candidate site will be indicated as a three-dimensional location superimposed on the heart tissue image. This significantly facilitates positioning a catheter at the candidate site by reference to the graphical indication, particularly when an image of the catheter is also visible in the heart tissue display.
In another aspect, the present invention provides an arrhythmia localization system comprising a database having known heart signals and associated discrete known ectopic or exit sites. A heart signal sensor array measures heart signals during an arrhythmia. A processor is coupled to the database and the sensor array. The processor calculates a candidate ectopic or exit site (which is different than the known sites) in response to the measured heart signals and the known heart signals.
Generally, the processor will comprise hardware, software, and/or firmware adapted to perform any or all of the methods of the present invention as described herein. Typically, the processor interpolates between a plurality of the known sites associated with the plurality of known heart signals based on the comparison of the measured heart signals to a plurality of the known heart signals, often using a statistical comparison algorithm. In many embodiments, a catheter (such as an ablation catheter and/or a pacing catheter) will be used with the system, a location of a distal portion of the catheter preferably being transmitted to the processor by a catheter position sensor.
While the invention is useful for absolute localization based on a database built up from many different patients, it is particularly beneficial for relative localization within a particular patient""s heart anatomy when the database comprises, at least in part, heart signals and known sites associated with that particular patient.